13.5.2.3. Move the data

Next we move the data from the old disk onto the new one.
Note that it is not necessary to unmount the file system
before doing this. Although it is *highly* recommended that
you do a full backup before attempting this operation in case
of a power outage or some other problem that may interrupt
it. The pvmove command can take a considerable amount of time
to complete and it also exacts a performance hit on the two
volumes so, although it isn't necessary, it is advisable to
do this when the volumes are not too busy.